If your wood door is sealed with varnish, it is important to refinish it regularly to protect it from sun and water damage. A timely and cost-effective alternative to stripping the door is a much simpler process that I have adapted: I lightly sand the door to remove dirt and mildew; I stain the wood to revitalize its natural color; lastly, I coat the door with spar urethane – a marine-quality varnish to protect the wood from harsh UV rays and heavy rain.